How Md Vpn Works - HP FlexNetwork 7500 Series Configuration Manual

How MD VPN works

This section describes default-MDT establishment, multicast traffic delivery based on the
default-MDT, and inter-AS MD VPN implementation.
For a VPN instance, multicast data transmission on the public network is transparent. The VPN data
is exchanged between the MTIs of the local PE and the remote PE. This implements the seamless
transmission of the VPN data over the public network. However, the multicast data transmission
process (the MDT transmission process) over the public network is very complicated.
Default-MDT establishment
The multicast routing protocol running on the public network can be PIM-DM, PIM-SM, or PIM-SSM.
The process of creating a default-MDT is different in these PIM modes.
In multicast VPN applications, the public network does not support BIDIR-PIM. For more information
about BIDIR-PIM, see
Default-MDT establishment in a PIM-DM network
Figure 64 Default-MDT establishment in a PIM-DM network
As shown in
instance A. The process of establishing a default-MDT is as follows:
To establish PIM neighboring relationships with PE 2 and PE 3 through the MTI in VPN
1.
instance A, PE 1 performs the following actions:
a. Encapsulates the PIM protocol packet of the private network into a public network multicast
data packet. PE 1 does this by specifying the source address as the IP address of the MD
source interface and the multicast group address as the default-group address.
b. Sends the multicast data packet to the public network.
This action triggers a flood-prune process on the public network. Other PE devices that
belong to VPN instance A are members of the default group. Each device along the
transmission path of the packet on the public network creates an (11.1.1.1, 239.1.1.1) state
entry. This forms an SPT with PE 1 as the root, and PE 2 and PE 3 as leaves.
At the same time, PE 2 and PE 3 separately initiate a similar flood-prune process.
2.
Finally, three independent SPTs are established in the MD, constituting a default-MDT in the PIM-DM
network.
"Configuring
Figure 64, PIM-DM is enabled on the network, and all the PE devices support the VPN
PIM."
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